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Subject[PATCH 4/5] x86-64: Replace vsyscall gettimeofday fallback with int 0xcc
Date
Now the only way to issue a syscall with side effects through the
vsyscall page is to call a misaligned instruction. I haven't
checked for that.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
---
arch/x86/include/asm/traps.h | 4 +++
arch/x86/include/asm/vsyscall.h | 6 +++++
arch/x86/kernel/entry_64.S | 2 +
arch/x86/kernel/traps.c | 4 +++
arch/x86/kernel/vsyscall_64.c | 47 ++++++++++++++++++++++++++++++++++-----
5 files changed, 57 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 0310da6..7eae1e4 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -1,6 +1,8 @@
#ifndef _ASM_X86_TRAPS_H
#define _ASM_X86_TRAPS_H

+#include <linux/kprobes.h>
+
#include <asm/debugreg.h>
#include <asm/siginfo.h> /* TRAP_TRACE, ... */

@@ -38,6 +40,7 @@ asmlinkage void alignment_check(void);
asmlinkage void machine_check(void);
#endif /* CONFIG_X86_MCE */
asmlinkage void simd_coprocessor_error(void);
+asmlinkage void intcc(void);

dotraplinkage void do_divide_error(struct pt_regs *, long);
dotraplinkage void do_debug(struct pt_regs *, long);
@@ -64,6 +67,7 @@ dotraplinkage void do_alignment_check(struct pt_regs *, long);
dotraplinkage void do_machine_check(struct pt_regs *, long);
#endif
dotraplinkage void do_simd_coprocessor_error(struct pt_regs *, long);
+dotraplinkage void do_intcc(struct pt_regs *, long);
#ifdef CONFIG_X86_32
dotraplinkage void do_iret_error(struct pt_regs *, long);
#endif
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index d555973..293ae08 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -31,6 +31,12 @@ extern struct timezone sys_tz;

extern void map_vsyscall(void);

+/* Emulation */
+static inline bool in_vsyscall_page(unsigned long addr)
+{
+ return (addr & ~(PAGE_SIZE - 1)) == VSYSCALL_START;
+}
+
#endif /* __KERNEL__ */

#endif /* _ASM_X86_VSYSCALL_H */
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 8a445a0..8e12f50 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1121,6 +1121,8 @@ zeroentry spurious_interrupt_bug do_spurious_interrupt_bug
zeroentry coprocessor_error do_coprocessor_error
errorentry alignment_check do_alignment_check
zeroentry simd_coprocessor_error do_simd_coprocessor_error
+zeroentry intcc do_intcc
+

/* Reload gs selector with exception handling */
/* edi: new selector */
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index b9b6716..d34894e 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -872,6 +872,10 @@ void __init trap_init(void)
set_bit(SYSCALL_VECTOR, used_vectors);
#endif

+ set_system_intr_gate(0xCC, &intcc);
+ set_bit(0xCC, used_vectors);
+ printk(KERN_ERR "intcc gate isntalled\n");
+
/*
* Should be a barrier for any external CPU state:
*/
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 3e8dac7..6135a28 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -32,6 +32,7 @@
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/notifier.h>
+#include <linux/syscalls.h>

#include <asm/vsyscall.h>
#include <asm/pgtable.h>
@@ -44,6 +45,7 @@
#include <asm/desc.h>
#include <asm/topology.h>
#include <asm/vgtod.h>
+#include <asm/traps.h>

#define __vsyscall(nr) \
__attribute__ ((unused, __section__(".vsyscall_" #nr))) notrace
@@ -92,13 +94,11 @@ static __always_inline void do_get_tz(struct timezone * tz)
*tz = VVAR(vsyscall_gtod_data).sys_tz;
}

-static __always_inline int gettimeofday(struct timeval *tv, struct timezone *tz)
+static __always_inline int fallback_gettimeofday(struct timeval *tv)
{
int ret;
- asm volatile("syscall"
- : "=a" (ret)
- : "0" (__NR_gettimeofday),"D" (tv),"S" (tz)
- : __syscall_clobber );
+ /* Invoke do_intcc. */
+ asm volatile("int $0xcc" : "=a" (ret) : "D" (tv));
return ret;
}

@@ -113,7 +113,7 @@ static __always_inline void do_vgettimeofday(struct timeval * tv)

vread = VVAR(vsyscall_gtod_data).clock.vread;
if (unlikely(!vread)) {
- gettimeofday(tv,NULL);
+ fallback_gettimeofday(tv);
return;
}

@@ -236,6 +236,41 @@ static void __cpuinit vsyscall_set_cpu(int cpu)
write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
}

+void dotraplinkage do_intcc(struct pt_regs *regs, long error_code)
+{
+ /* Kernel code must never get here. */
+ if (!user_mode(regs))
+ BUG();
+
+ local_irq_enable();
+
+ if (!in_vsyscall_page(regs->ip)) {
+ struct task_struct *tsk = current;
+ if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
+ printk_ratelimit()) {
+ printk(KERN_INFO
+ "%s[%d] illegal int $0xCC ip:%lx sp:%lx",
+ tsk->comm, task_pid_nr(tsk),
+ regs->ip, regs->sp);
+ print_vma_addr(" in ", regs->ip);
+ printk("\n");
+ }
+
+ force_sig(SIGSEGV, current);
+ return;
+ }
+
+ if (current->seccomp.mode) {
+ do_exit(SIGKILL);
+ return;
+ }
+
+ regs->ax = sys_gettimeofday((struct timeval __user *)regs->di, NULL);
+
+ local_irq_disable();
+ return;
+}
+
static void __cpuinit cpu_vsyscall_init(void *arg)
{
/* preemption should be already off */
--
1.7.5.1


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